TREX GEAR Ratios FOR scale ops
Main Gear and Tail Ratios
When I first got into scale flying I was directed to the Align TREX 600ESP as a good set of mechanics which were easily put into most scale fuselages. Since then I have built 3 sets of 600ESPs and three sets of the Align TREX 700E FBL mechanics for use in scale helicopters. As a result of this I have became very familiar with what the TREX platform could offer to scale builds - succesfully using a set of TREX 700E FBL mechanics in a (40lb) Vario BK-117 1/5 scale heli (no longer shown in the chart since it was sold, it uses the same numbers as the Vario MD500E - 900) .
I use Castle Creations Phoenix 80HV and 120HV ESCs in all my helis. These are NOT freewheeling ESCs and as such target RPM is ideally acheived between 85% and 93% ESC output as per Castle's recommendation. Having said that, even running as low as 80% presented no heating issues for the ESC.
I have accumulated a database/chart of possible gear ratios that can be acheived with the TREX gearing options combined with fairly common KV motor ratings.
(NOTE: I use 10s on all my helis as it does make it easier to get the lower scale headspeeds from the gear combos)
The chart also shows the heli size and weight with Headspeed RPMs I use, which give me (IMO) good performance.
TREX Gear Colors:
White: oldest, weakest of the materials used. I recommend avoiding them altogether.
Black: replaced the White gears as a stronger option.
Red: replaces Black gears in the Tail Box and Tail Drive. Stronger than the Black gears.
Blue: Replaces the bevel gears on the Umbrella gear and Tail Drive gears. Stronger than the Red.
MOD1.0 gear sets - recommended for the heavier helicopters.
Trex offers a thicker MOD1.0 Main Gear at 13mm vs. the original 10mm. Recommended for heavier helicopters as well.
Here's the chart
Tail Ratios:
Here is a chart of the TREX tail ratios for both 600 and 700 size mechanics. The 600 and 700 tail systems have many interchangeable parts including the same diameter boom and torque tubes, so some of these can be mixed and matched.
Align 600 available Tail ratios
Align M0.8 Torque Tube Front Drive Gear Set (34T)
Align M0.8 Autorotation Tail Drive Gear (Black) (131T)
Head1400rpm = 5394rpm Tail
Head 2050rpm = 7900rpm tail
Align M0.6 Torque Tube Front Drive Gear Set (40T
Align Autorotation Tail Drive Gear Set (Black) (180T)
Head 1400rpm = 6300rpm tail
Head 2050rpm = 9225rpm tail
Align 700 MOD1.0 Tail ratios
Tail Speed Gear Sets Combinations
102T/23T M1 1:4.43
104T/22T M1 1:4.73
104T/21T M1 1:4.95
105T/20T M1 1:5.25
-4.43 = 4430
-4.73 = 4730
-4.95 = 4950
-5.25 = 5250 @1500rpm
-4.43 = 6645
-4.73 = 7095
-4.95 = 7425
-5.25 = 7875